The present invention relates to an isolation valve useful in, among other things, fuel tank emission control systems.
Fuel vapor emission control systems are becoming increasingly more complex, in large part in order to comply with environmental and safety regulations imposed on manufacturers of gasoline-powered vehicles, particularly light passenger trucks and cars. Along with the ensuing overall system complexity, complexity of individual components within has also increased.
Certain regulations affecting the gasoline-powered vehicle industry require that fuel vapor emission from a fuel tank's ventilation system be stored during periods of an engine's operation. In order for the overall vapor emission control system to continue to function for its intended purpose, periodic purging of stored hydrocarbon vapors is necessary during operation of the vehicle.
During purges, all vapor pathways are open to a canister where hydrocarbon vapors are stored. Pressure or flow fluctuations can negatively impact efficiency, effectiveness, and exhaust emissions of an engine during operation based on the impact that such pathways have on purging. In order to remove any such effects, some of which are undesirable, imposed by an open vapor pathway to a fuel tank when purging an adjacent canister, fuel tank isolation valves have been used.
Certain mechanically actuated (e.g. in response to pneumatic pressure) valves are known. For example, see U.S. Pat. No. 4,714,172. However, current trends in fuel tank emission control systems tend to include electronically actuated valves. U.S. Pat. No. 6,668,807 describes a fuel vapor emission control system employing a fuel tank isolation valve. The fuel tank isolation valve is electronically actuated. Electrically actuated valves were purportedly developed to overcome disadvantages known to be associated with conventional diaphragm-actuated valves. Thus, present fuel tank emission control systems rely heavily on electrically actuated valves. For example, see the discussion of electrically actuated valves in U.S. Pat. No. 6,553,975. U.S. Pat. No. 6,637,261 discusses further electrically actuated valves used in fuel tank emission control systems.
A wide variety of components can be joined to form a workable fuel tank emission control system. One conventional fuel tank emission control system is illustrated in prior art FIG. 1. The fuel tank emission control system includes a hydrocarbon storage device (i.e., canister) 1 connected to receive hydrocarbon fuel vapor directly from the fuel tank 2 via an unobstructed pathway, with the canister 1 having an atmospheric purge valve 3 that may be opened or closed by a control valve 4 connected to an electronic control unit (ECU) 5. The fuel tank 2 has a tank pressure sensor 6 connected to sense the internal pressure in the tank 2 and provide an associated electrical input to the ECU 5 based thereupon.
The canister 1 has a vapor outlet line 7 connected to provide hydrocarbon vapor flow for internal combustion in an engine downstream. Hydrocarbon vapor flows via vapor outlet line 7 from canister 1 through a control orifice 8, with the downstream side of orifice 8 being connected to the inlet of an engine purge control valve 9 having its outlet connected to the combustion air inlet or intake manifold of an engine 10. Engine purge control valve 9 is an electrically actuated valve controlled by the ECU 5.
An electronically actuated, normally open valve 11 is connected to bypass the control orifice 8 and is also controlled by the ECU 5. A differential pressure sensor 12 is connected to sense the pressure drop across the control orifice 8 and provide an associated electrical input signal to the ECU 5.
Recent innovations in fuel tank emission control systems, including transformation of valves therein from mechanical to electrical actuation, have not always resulted in overall system advantages. For example, as more and more components within vehicles are designed to be electronically controlled, the overall cost of the vehicle has increased. Further, the great reliance placed on use of electrical components for performing individual functions is predicated on proper functioning of electrical systems. A small interruption in the electrical system can thus have widespread impact throughout the overall operating system of a vehicle. When the interruption affects proper opening and closing of fuel tank isolation valves therein, the impact can even spread so far as to cause undesirable or even unlawful release of contaminants into the environment or result in mechanical failure of an associated engine. Improved fuel tank isolation valves are thus desired.